The proliferation of wireless technologies is leading to wireless terminals that incorporate different modems for multiple wireless interfaces. In many situations it is necessary to operate two or more of wireless interfaces simultaneously. Depending on the operating frequencies of the wireless interfaces, the terminal can experience interference due to the simultaneous operation of the wireless interfaces. Specifically, the transmitting signals on one interface results in interference being experienced in the reception of signals on the other interface. This problem is commonly known as “Interference due to In-device Coexistence” of multiple interfaces.
This problem has been discussed in 3GPP specifically for the coexistence of 3GPP LTE with certain technologies that operate in the Industrial-Scientific-Medical (ISM) band. Of particular interest are situations where the LTE frequency band is adjacent to the ISM band. For example, TDD LTE band 40 (2300-2400 MHz) and FDD LTE Band 7 (uplink) are adjacent to the ISM band (2400-2483.5 MHz). The ISM band is available for unlicensed operation. Technologies that operate in the ISM band include IEEE 802.11 (also known as “WLAN” or “WiFi”) and IEEE 802.15 and its variants (popularly known as Bluetooth). Some studies have shown that the interference that occurs between band 40 and the ISM band is severe. Such coexistence interference scenarios may also occur due to second harmonics of radio access technologies (RATs) supporting uplink transmissions in the 2.5-2.9 GHz bands (e.g., LTE Band 7, Band 38, LTE TDD in 2600 MHz for US) and 5 GHz ISM band systems such as WLAN.
As indicated in 3GPP technical document RP-100671, the problem cannot be remedied solely using RF filters as filter technology does not provide sufficient rejection of adjacent frequencies. 3GPP has launched efforts to study solutions to this problem.
Therefore a need is seen for methods and apparatus that eliminate or reduce the coexistence problems described above while ensuring reasonable operating efficiency.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.